1. Field of the Invention
The present invention relates to a bonding agent for bonding two conductive connection members.
2. Description of the Related Art
A cell (single cell) of a solid oxide fuel cell (SOFC) includes a solid electrolyte, a fuel electrode formed integral with the solid electrolyte, and an air electrode formed integral with the solid electrolyte. A fuel gas (hydrogen gas, etc.) is supplied to the fuel electrode of the SOFC cell and a gas (air, etc.) containing oxygen is supplied to the air electrode of the SOFC cell, whereby a chemical reaction represented by Formulas (1) and (2) described below is generated. Thus, a potential difference is produced between the fuel electrode and the air electrode. This potential difference is based upon an oxygen conductivity of the solid electrolyte.(½).O2+2e−→O2−(at air electrode)  (1)H2+O2−→H2O+2e−(at fuel electrode)  (2)
In the SOFC, a conductive connection member (hereinafter referred to as interconnector) for collecting electric current is bonded and fixed to each of the fuel electrode and the air electrode with a bonding agent. Power based upon the potential difference is taken out to the outside through the respective interconnectors. Attention is particularly focused on the bonding between the air electrode and the interconnector below.
An expensive Pt material has conventionally been used as the bonding agent to bond the air electrode and the interconnector so as to electrically connect the air electrode and the interconnector. A silver material from a metal and a conductive ceramic material from a ceramic are considered as a substitute material for the Pt material in order to reduce cost. For example, Japanese Unexamined Patent Application No. 2005-339904 discloses La—Sr—Co—Fe perovskite complex material as a conductive ceramic material for fixedly bonding the air electrode and the interconnector.